This invention relates to a method and apparatus for installing a cellular telephone in a vehicle such as an automobile and in particular to such a method and apparatus that avoids outward visual indications of a cellular telephone in the vehicle.
A vexatious problem with the use of two-way mobile communication equipment, such as citizen band transceivers and cellular telephones, installed in vehicles such as automobiles, is the need for a special-purpose antenna that externally indicates the presence of expensive equipment in the vehicle and thus increases the risk of theft. Such a specialized antenna is provided because the two-way mobile communication equipment operates in a distinctly different frequency band from the FM receiver and antenna design is strongly dependent on the frequency band of the signal being transmitted and/or received.
The desirability of disguising the existence of mobile communication equipment in a vehicle is well recognized in the art and extensive efforts have been put forth to eliminate antennas that are special-purpose in appearance. One common approach is to provide an adapter circuit to allow a citizens band (CB) tranceiver, as well as the FM broadcast receiver (radio) to utilize the existing antenna for the FM receiver. Because a CB transceiver operates in the 27 MHz band, which is lower than the 88-108 MHz band of the FM receiver, a loading coil is provided in the leg of a three-leg adapter extending to the CB transceiver. The loading coil is provided to increase the effective length of the antenna, as viewed by the CB transceiver, while the path from the antenna to the FM receiver is substantially unaffected. Such an approach is disclosed in U.S. Pat. No. 3,259,901 to R. O. Bykerk.
A second approach to disguising the existence of a CB transceiver is to replace the existing FM receiver stick antenna with a special-purpose antenna which has the appearance of an FM radio antenna, but in fact, has structure that facilitates optimum operation with both the radio and the two-way mobile communication equipment. Such devices, however, are expensive and impractical for after-market field installation due to extensive labor required to remove the existing radio antenna and install the replacement device. An example of such a device is disclosed in U.S. Pat. No. 4,506,266 issued to Mizuno et al., in which a specialized antenna has a control system that responds to the position of an equipment selector switch to adjust the length of the antenna by motor means in order to have a capture-length equal to one-quarter wavelength of the signal frequency of the equipment being operated.
A cellular telephone is a special type of mobile communication transmitter/receiver (transceiver) that communicates with the geographically closest one of a series of interface cells or stationary transceivers which are spaced approximately 20 miles apart in a grid and interconnected with the telephone network. In contrast to a citizens band transceiver, which operates at a frequency lower than an FM radio, a cellular telephone operates at a frequency substantially higher than an FM radio. Therefore, techniques for adapting a CB transceiver to an existing vehicle radio system are ineffective in adapting a cellular telephone to a vehicle because there are no known means for shortening the effective length of an antenna to provide a quarter-wavelength antenna capture-length for the cellular telephone.
A need for an effective means to eliminate outward visual indications of the existence of the cellular telephone is all the greater because a cellular telephone is significantly more expensive than a citizens band transceiver. The average cost of a celelular telephone is $650-$950 and may range as high as $1900. A specialized multiband antenna has been proposed in U.S. Pat. No. 4,675,687 to James Elliott for use with an FM radio and a cellular telephone. The Elliott antenna is, however, too costly for after-market installation for reasons previously stated. Thus, the need for means that can be used with field-installed equipment for eliminating the separate cellular telephone antenna has not been met.